Obamacare will not be repealed — perhaps not ever — if Democratic nominee Hillary Clinton wins the White House, House Speaker Paul D. Ryan warned Monday in a last-minute pitch to GOP voters.

Mr. Ryan, Wisconsin Republican, said the future of the country “is on the line” and that President Obama’s health overhaul could be cemented and even expanded if Republicans lose on Election Day.

The speaker was responding to Milwaukee radio host Jay Weber, who said the Affordable Care Act “doesn’t get repealed, likely ever, if Hillary wins.”

“Yes, yeah, I do agree. I do agree,” Mr. Ryan said. “Hillary’s talking about a public option, which is basically double down on government-run healthcare. That’s the opposite of what we’re offering. We actually have a plan to replace Obamacare. All of us have basically gotten a consensus on what our plan is, but we have to win an election to put it in place.”

Mr. Ryan is hoping to work with GOP presidential nominee Donald Trump to repeal Obamacare and replace its heavy mandates and coverage requirements with Republican reforms that rely on free-market levers to incentivize people into buying coverage.

He said that won’t be possible if Mr. Trump and down-ballot candidates don’t win.

“I think we need to unify as a party, I think we need to get everybody to the polls,” Mr. Ryan said.

Mr. Trump’s personal feuds and strident views on immigration and trade have riled GOP leaders for months, however, and the mogul’s lewd, “hot mic” remarks from an “Access Hollywood” taping in 2005 presented new peril.

Mr. Ryan, who’d chastised Mr. Trump for his proposed Muslim ban and comments about an Indiana-born judge of Mexican heritage, said he would no longer defend Mr. Trump or campaign with him after the tape was leaked in early October.

Some conservatives chastised Mr. Ryan for his lukewarm approach to Mr. Trump, placing his future as speaker in doubt.

Yet Mr. Ryan says he voted for the GOP nominee, and he’s repeatedly rebuked Mrs. Clinton for using a private email server at the State Department. He says she risked national security, even if the FBI cleared her for a second time over the weekend.

In a statement Sunday, Mr. Ryan told Americans to “bring the Clinton era to an end by voting for Donald Trump on Tuesday.”

Still, Mr. Ryan has mainly focused on preserving the GOP’s House majority and its 54-46 edge in the Senate.

Mr. Ryan has been stumping hard for Sen. Ron Johnson, Wisconsin Republican who’s locked in a tight race with the Democratic he unseated in 2010, Russ Feingold.

Mr. Ryan said the Wisconsin Senate race would likely as a bellwether for whether the GOP can hold the chamber.

“People need to go vote. The future of your country is on the line, and good people like Ron Johnson, who are in very, very tight races — that will be determine by whether or not people get up and go vote,” Mr. Ryan told Mr. Weber.